A laser has many components. Because a laser is a precision instrument, many of these components must be of high precision. One such component is the optical resonator structure. The optical resonator structure has a cavity in which the active lasing medium is excited to produce the beam of coherent radiation. At one end of the optical resonator cavity is a first highly polished mirror, which is nearly one hundred percent (100%) reflective; a second highly polished mirror is at the other end, which is less reflective than the first mirror and permits some of the radiation to be transmitted as useful output therethrough. In conventional gas lasers of the axial flow type, a gaseous lasing medium flows in the optical resonator generally parallel to the optical resonator's longitudinal axis. One or more anode-cathode pairs each introduce an electric field in the flowing gas to create a volume of plasma, sometimes referred to as the "discharge region" or "discharge volume," in the optical resonator. The contents of the optical resonator are heated by the electric field. Accordingly the purpose for circulating gas within the resonator is to remove heated gas and substitute cooler gas therefor. The removed gas (which may be a pure gas or a mixture of gasses) is typically cooled in a heat exchanger and recycled for use in the resonator.
In axial gas flow lasers, it is desirable to maintain uniform gas flow, so that the discharging volume does not irregularly move within the resonator, and so that the discharge region is not limited to an undesirably small portion of the resonator cavity (such as, for example, within a small distance from the longitudinal axis of the resonator tube). If the discharge volume moves irregularly, the laser's coherent radiation output will vary accordingly. If the discharge volume is too small, the maximum output of the laser is accordingly limited.
Conventional means for achieving uniform gas flow in an axial flow gas laser have included bulky gas inlet means having complicated design. It has not been known until the present invention how to achieve stable, uniform gas flow in an axial gas flow laser by a simple structure in which a single orifice serves a dual function as the inlet through which gas may enter the resonator, and at which a rod-type electrode may be positioned in electrical communication with the entering gas.